Computer-aided design programs allow designers to draft, edit, analyze and test designs with the speed and accuracy of powerful desktop computers. While the designer is working, the computer sends its output to the computer screen, to be viewed by the designer. To facilitate input, a digitizing pad, information overlay and an input selector are used. The information overlay is imprinted with a "menu graphic." The menu graphic is a drawing consisting of various computer commands and symbols, arranged on the information overlay so that when the information overlay is laid upon the digitizing pad, the location of each command in relation to the digitizing pad is known to the computer. The input selection device is commonly called a "cursor" or a "puck." The cursor is placed upon the information overlay, and the computer knows its position on the digitizing pad. To use any particular command of the menu graphic, the operator need only place the window of the cursor over the command and push a button on the cursor. Since the computer knows the position of the cursor on the digitizing pad and since that position corresponds to a command of the menu graphic, the computer then knows that the operator has chosen the particular command. The computer then executes the command.
This system is also used for drawing in much the same way: The operator uses the cursor to draw on a "drawing area" of the information overlay. This drawing area corresponds to a drawing area known to the computer, and the computer displays the drawing on its screen as the operator draws. While this system enhances efficiency of input compared to typed input or on-screen windows, it creates several ergonomic problems of its own which prevent optimum operator comfort and efficiency.
First, the information overlay usually consists of a piece of white paper with the menu graphic imprinted in black ink. This requires a relatively bright lighting environment for comfortable viewing. However, the computer screen with which the information overlay is used is difficult to read in bright light and is best used in low light to make the computer screen legible. But then the operator must strain to see the information overlay. Conversely, operators may work in bright light to make the digitizing pad legible, but then they must strain to read the computer screen. Another alternative, spotlighting the information overlay in a low light environment, creates sharply contrasting light levels and glare which cause eye fatigue.
Second, the information overlay is designed to be used on the same desktop as the computer; it lies flat on the table while the computer screen is upright. This arrangement makes it easy and comfortable for the hand and arm to manipulate the cursor, but makes the information overlay difficult to read because it is distant and viewed at an angle. Operators may currently sit comfortably to view the computer screen and strain to see the information overlay. Conversely, operators may sit comfortably to view the information overlay and strain to see the computer screen. Lifting the digitizing pad to a vertical plane near the computer screen makes it difficult to keep the information overlay in place and makes use of the cursor difficult and tiresome.